Medical devices often must be shielded from interacting with body fluids in vivo. For example, for devices that are electrical in nature, for example, such as pacemakers and other “active” implants for sensing, delivery of therapeutics and/or active control of various bodily functions should be protected.
One prevalent method used to provide this protection is to weld the device inside a titanium or other biocompatible metal “can.” Another method to provide the shield necessary to protect a medical device from interaction with bodily fluids in vivo is polymer coating the device. Polymer coating such “active” implants has significant technical challenges and limitations which have made polymer coatings relatively unsuccessful as a means of sealing the devices.
For example, one limitation of traditional coating processes in providing a seal is that traditional polymer coating processes (e.g. dip, spray, etc.) all require the use of a solvent-based system. Exposing the device to a solvent causes problems in the device. Furthermore, there are inherent challenges with effective drying of solvent-based polymer coatings.
Solvent-less coating processes (e.g. vapor deposition, plasma deposition, dry powder coating, etc.) also have limitations in providing seals to active devices. Solvent-less coating processes all require very aggressive conditions that could damage the device—such as elevated temperatures to cure a dry powder coated device.
Additionally, for most current coating technologies, solvent-based and solvent-less, it is often difficult to achieve coatings of uniform thicknesses and prevent the occurrence of defects (e.g. bare spots, webs, pools, clumps). As the size of the substrate decreases, and as the mechanical complexity increases, it grows increasingly difficult to uniformly coat all surfaces of a substrate. Supplemental steps, therefore, are sometimes necessary to assure proper coating, including, for example, multiple coating steps and/or drying between or after the coating steps (in solvent-based systems).
Conventional polymer films likewise have limitations in providing a seal. Conventional polymer films are known to be quite ineffective barriers to the transport of gaseous materials. While this is especially true of small molecule gases, the problem extends to providing a barrier to water vapors and other gases that could deleteriously effect an electrical biomedical implant.